The use of the existing heat pump drying method drum type washing and drying machine or dryer. In a low-temperature environment, such as 0° C., from drying machine drying start stage, the temperature of the air blown out from the outer cylinder is close to 0° C. because the water temperature of the rinsing clothes is only slightly higher than 0° C. In this case, the saturation temperature of the refrigerant medium in the heat pump system under saturated pressure is much lower than 0° C., which results in the compressor of the heat pump system operating at low load and low input power, and the temperature rise in the outer cylinder is extremely slow, making the laundry drying efficiency is low. If the evaporation temperature of the refrigerant medium in the heat pump system in the evaporator maintains in a low temperature environment of below 0° C. for a long period of time, it will lead to the evaporator and the humid air blowing out of the outer cylinder in contact and a lot of frosting occur on the surface of the evaporator fin and decreasing the effective area of the evaporator and will block the cycle of the air circulation cycle, so that refrigerant medium of the compression system in the evaporator cannot be completely vaporized. The refrigerant medium in the liquid state enters the compressor along the suction pipe of the compressor, resulting in a failure of the compressor.
To solve the foregoing problem, some improvements schemes are put forward, for example:
A heat pump system with an auxiliary heat source which disclosed in the Chinese Patent Application No. CN201120558843 comprises a refrigeration compressor, an evaporator, a condenser, a throttling device, and an auxiliary heating device, and an auxiliary heating device is arranged on the auxiliary heating device on the air duct at the back end of the condenser outlet. When the ambient temperature is low, heat pump efficiency is low, the heating temperature will be relatively low, this time, the auxiliary heating device can be turned on to shorten the drying time. Thus, the auxiliary heating means is added behind the condenser, and the air heated by the condenser is reheated by the heating means to raise the temperature of the air flow in the drying air path so that the evaporator attains a higher ambient temperature to raise the activity of refrigerant medium in the heat pump system, to improve the efficiency of drying purposes. However, in this way, the need to increase in the drying duct heating devices and some structural parts, to a certain extent, increased a wind resistance in the air drying wind path, easy to affect the drying effect at room temperature.
In view of the foregoing, the present invention is proposed.